Electronic battery tester with automatic compensation for low state-of-charge

ABSTRACT

Three embodiments of an improved electronic device for testing or monitoring storage batteries that may be only partially charged are disclosed. The device determines the battery&#39;s small-signal dynamic conductance in order to provide either a proportional numerical readout, displayed in appropriate battery measuring units, or a corresponding qualitative assessment of the battery&#39;s relative condition based upon its dynamic conductance and electrical rating. Without additional user intervention, the device also determines the battery&#39;s terminal voltage in an essentially unloaded condition and utilizes this information to automatically correct the measured dynamic conductance. By virtue of this automatic correction, the quantitative or qualitative information displayed to the user conforms with that of a fully-charged battery even though the battery may, in actual fact, be only partially charged. If the battery&#39;s state-of-charge is too low for an accurate assessment to be made, no information is displayed. Instead, an indication is made to the user that the battery must be recharged before testing.

This is a continuation of application Ser. No. 08/292,925, filed Aug.18, 1994, now abandoned, which is a continuation of application Ser. No.07/877,646, filed May 1, 1992, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to an electronic measuring or monitoring devicefor assessing the ability of a storage battery to deliver power to aload. More specifically, it relates to improved apparatus of the typedisclosed previously in U.S. Pat. Nos. 3,873,911, 3,909,708, 4,816,768,4,825,170, 4,881,038, and 4,912,416 issued to Keith S. Champlin.

Storage batteries are employed in many applications requiring electricalenergy to be retained for later use. Most commonly, they are employed inmotor vehicles utilizing internal combustion engines. In suchapplications, energy stored by "charging" the battery during engineoperation is later used to power lights, radio, and other electricalapparatus when the engine is stopped. The most severe demand upon thebattery of a motor vehicle is usually made by the starter motor. Failureto supply the starter motor with sufficient power to crank the engine,particularly in cold weather, is often the first indication of batterydeterioration. Clearly, a simple measurement that accurately assesses abattery's ability to supply cranking power is of considerable value.

Prior to the introduction of the dynamic conductance testing methoddisclosed in the six U.S. patents enumerated above, the method mostgenerally available for assessing a battery's ability to supply crankingpower was the standard load test. This test subjects a battery to aheavy dc current having a predetermined value dictated by the battery'srating. After a prescribed time interval, the battery's voltage underload is observed. The battery is then considered to have "passed" or"failed" the load test according to whether its voltage under load isgreater, or less, than a particular value.

Although the standard load test has been widely used for many years, ithas several serious disadvantages. These include:

1. The test draws a large current and therefore requires apparatus thatis heavy and cumbersome.

2. Considerable "sparking" can occur if the test apparatus is connectedor disconnected under load conditions. Such "sparking" in the presenceof battery gasses can cause an explosion with the potential for seriousinjury to the user.

3. A standard load test leaves the battery in a significantly reducedstate-of-charge and therefore less capable of cranking the engine thanbefore the test was performed.

4. The battery's terminal voltage decreases with time during performanceof the load test. Accordingly, test results are generally imprecise andoften dependent upon the skill of the operator.

5. Load test results are not repeatable since the test itselftemporarily polarizes the battery. Such test-induced polarizationsignificantly alters the initial conditions of anysubsequently-performed tests.

A practical alternative to the standard load test is taught in the sixU.S. Patents enumerated above. These documents disclose electronicapparatus for accurately assessing a battery's condition by means ofsmall-signal ac measurements of its dynamic conductance. They teach thata battery's dynamic conductance is directly proportional to its dynamicpower--the maximum power that the battery can deliver to a load. Dynamicconductance is therefore a direct measure of a battery's ability tosupply cranking power. In comparison with the load test method ofbattery appraisal, the dynamic conductance testing method has manyadvantages. For example, dynamic conductance testing utilizes electronicapparatus that is small and lightweight, draws very little current,produces virtually no sparking when connected or disconnected, does notsignificantly discharge or polarize the battery, and yields accurate,highly reproducible, test results. Virtually millions of batterymeasurements performed over the years have fully corroborated theseteachings and have proven the validity of this alternative testingmethod.

One disadvantage, however, of the dynamic conductance testing method hasbeen the fact that test results are somewhat dependent upon thebattery's state-of-charge. Accordingly, the methods and apparatusdisclosed in the first five of the six U.S. patents cited above havegenerally required that the battery be essentially fully charged to betested. Since many batteries are, in fact, fairly discharged when theyare returned for replacement under warranty, or when they are otherwisesuspected of being faulty, it has been frequently necessary to rechargea battery before testing it. Such recharging is costly andtime-consuming. Clearly, a simple method for performing accurate dynamicconductance tests on batteries "as is"--batteries that may be onlypartially charged--would be of considerable benefit.

Great progress toward solving this problem has been engendered by themethods and apparatus disclosed in the sixth U.S. patent cited above;U.S. Pat. No. 4,912,416. As is well known to those skilled in the art, abattery's state-of-charge is directly related to its open-circuit(unloaded) terminal voltage. By utilizing this fact, along withextensive experimental data, an empirical relationship was establishedbetween a battery's state-of charge, as reflected by its open-circuitvoltage, and its relative dynamic conductance, normalized with respectto its fully-charged value. This empirical relationship was firstdisclosed in U.S. Pat. No. 4,912,416. Further, apparatus disclosedtherein utilized this empirical relationship, along with measurements ofopen-circuit voltage, to appropriately correct dynamic conductancereadings--thus yielding battery assessments that were essentiallyindependent of the battery's state-of-charge.

However, the measuring apparatus disclosed in U.S. Pat. No. 4,912,416utilized an inconvenient two-step testing procedure requiringintermediate interaction by the user. The battery's open-circuit voltagewas first measured. Next, using the results of the voltage measurement,the user adjusted a variable attenuator to an appropriate setting.Finally, the dynamic conductance was measured. By virtue of thepreviously adjusted variable attenuator, the quantitative or qualitativedynamic conductance information ultimately displayed to the userconformed with that of a fully-charged battery even though the batterymay, in actual fact, have been only partially charged when tested.

The state-of-charge problem was thus solved in principle by the methodsand apparatus taught in U.S. Pat. No. 4,912,416. The required procedurewas somewhat inconvenient, however. It is therefore quite apparent thatimproved apparatus which provides automatic state-of-chargecorrection--a correction not requiring intermediate interaction by theuser--would be highly advantageous. Just such improved electronicbattery testing apparatus, providing automatic compensation for lowstate-of-charge, is disclosed herein below.

SUMMARY OF THE INVENTION

Three embodiments of an improved electronic device for testing ormonitoring storage batteries that may be only partially charged aredisclosed. The device determines the battery's small-signal dynamicconductance in order to provide either a proportional numerical readout,displayed in appropriate battery measuring units, or a correspondingqualitative assessment of the battery's relative condition based uponits dynamic conductance and electrical rating. Without additional userintervention, the device also determines the battery's terminal voltagein an essentially unloaded condition and utilizes this information toautomatically correct the measured dynamic conductance. By virtue ofthis automatic correction, the quantitative or qualitative informationdisplayed to the user conforms with that of a fully-charged battery eventhough the battery may, in actual fact, be only partially charged. Ifthe battery's state-of-charge is too low for an accurate assessment tobe made, no information is displayed. Instead, an indication is made tothe user that the battery must be recharged before testing.

The electronic battery testing/monitoring device with automaticcompensation for low state-of-charge hereof can be used to obtain eithera qualitative or quantitative assessment of a wide variety ofelectrochemical energy sources other than lead-acid batteries. Forexample, single electrochemical cells can be tested or monitored in amanner identical to that applied to testing or monitoring batteries ofseries-connected cells. Furthermore, by utilizing appropriate numericalcorrection factors, the invention can be used to test or monitor otherelectrochemical energy sources such as alkaline, nickel-cadmium, orlithium cells and batteries. The invention hereof is widely applicableto such testing or monitoring of energy sources by virtue of itssimplicity, its safety, its accuracy, its ease of operation, and its lowcost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the Thevenin's equivalent circuit of a lead-acid storagebattery comprising its open-circuit voltage, V_(o), and its internalresistance, R_(x), connected in series.

FIG. 2 is an empirical plot of normalized dynamic conductance, G_(x),versus open-circuit voltage, V_(o), showing the correlation withmeasurements performed upon four different lead-acid storage batterieshaving differing electrical ratings and fabricated by differentmanufacturers.

FIG. 3 is a simplified block diagram of an improved electronic batterytesting/monitoring device employing automatic compensation for lowstate-of-charge in accordance with a first embodiment of the presentinvention.

FIG. 4 is a graphical plot of the state-of-charge correction factorobtained by taking the reciprocal of the empirical normalized dynamicconductance curve of FIG. 2.

FIG. 5 is a plot of a four-segment piecewise-linear approximation to thecorrection factor curve of FIG. 4 implemented by the correctionamplifier circuit disclosed in FIG. 6.

FIG. 6 is a schematic diagram of a dc correction amplifier embodimentwhich implements the four-segment piecewise-linear transfer functiondisclosed in FIG. 5.

FIG. 7 is a complete schematic diagram of an improved electronic batterytesting/monitoring device with automatic compensation for lowstate-of-charge configured for testing/monitoring 12-volt automotivebatteries in accordance with a first embodiment of the presentinvention.

FIG. 8 is a simplified block diagram of a second embodiment of animproved electronic battery testing/monitoring device with automaticcompensation for low state-of-charge.

FIG. 9 is a simplified block diagram of a third embodiment of animproved electronic battery testing/monitoring device with automaticcompensation for low state-of-charge.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the Thevenin's equivalent circuit of alead-acid storage battery is shown. In this equivalent representation,the battery is described by its open-circuit voltage, V_(o), and itsinternal resistance, R_(x), connected in series.

As has been fully disclosed in the first five of the six U.S. Patentscited above, a conventional dynamic conductance battery test of afully-charged battery traditionally ignores the open-circuit voltage,V_(o). Instead, the electronic test apparatus directly measures thebattery's dynamic conductance G_(x) =1/R_(x). The testing/monitoringdevice then provides the operator with either a numerical readoutdisplayed in proportional battery measuring units (such as "ColdCranking Amps", "Ampere-Hours", or "Watts"), or else with a qualitativedisplay ("Pass/Fail") based upon comparing the measured value of G_(x)with a corresponding reference value determined from the battery'selectrical rating and temperature.

Although the open-circuit voltage, V_(o), has not been normally used indynamic conductance testing of fully-charged batteries, it has beenpreviously used to determine state-of-charge. As is well known to thoseskilled in the art, a battery's state-of-charge is directly related toits open-circuit (unloaded) terminal voltage. For example, withautomotive-type lead-acid batteries having a nominal voltage of 12volts, the open-circuit voltage is known to vary from about 11.4 volts,for batteries that are virtually totally discharged, to about 12.6volts, for batteries that are nearly fully charged.

FIG. 2 shows the observed relationship between normalized dynamicconductance and open-circuit voltage appropriate to a large class ofautomotive-type lead-acid storage batteries. This information wasdisclosed previously in U.S. Pat. No. 4,912,416. FIG. 2 displays anempirical graph of relative dynamic conductance, normalized with respectto the fully-charged value, G_(x) (V_(o))/G_(x) (12.6), plotted as afunction of open-circuit voltage, V_(o). The solid curve plotted in FIG.2 is described by a second-order polynomial equation having coefficientsadjusted to best fit the experimental data. The appropriately adjustedpolynomial equation is: ##EQU1##

FIG. 2 also discloses normalized experimental points which representactual measurements obtained from four different batteries possessingdifferent electrical ratings and fabricated by different manufacturers.Batteries XM0, XM1, and XM3 are six-cell batteries having nominalvoltages of 12 volts. Battery XM2 is actually a three-cell, 6-voltbattery. Open-circuit voltage measurements of battery XM2 weremultiplied by a factor of two in order to plot XM2 data points on thesame graph as the other three batteries. One sees that the normalizedmeasurements obtained from all four batteries agree quite closely withthe empirical relation described by Equation 1. The fact that the sameempirical relation shows strong correlation with experimental dataobtained from both 6-volt and 12-volt batteries indicates that theempirical state-of-charge correction disclosed in FIG. 2 is quiteuniversal and is actually a fundamental property of a single cell.

Referring now to FIG. 3, a simplified block diagram of a firstembodiment of an improved electronic battery testing/monitoring devicewith automatic compensation for low state-of-charge is disclosed. Exceptfor specific details having to do with the circuitry for automaticcompensation for low state-of-charge, the explanation of the operationof the block diagram of FIG. 3 is identical with that of thecorresponding block diagram referred to as FIG. 1 in U.S. Pat. No.4,816,768.

Accordingly, signals representative of the signal at output 10 ofhigh-gain amplifier cascade 12 are fed back to input 20 of high-gainamplifier cascade 12 by means of two feedback paths; internal feedbackpath 14 and external feedback path 16. Internal feedback path 14includes low pass filter (LPF) 18 and feeds a signal directly back toinput 20 of high-gain amplifier cascade 12. The purpose of internalfeedback path 14 and low pass filter 18 is to provide large dc feedbackbut relatively little ac feedback in order to define the operating pointof high-gain amplifier cascade 12 and ensure its dc stability withoutappreciably reducing its ac voltage gain. External feedback path 16contains resistive network 22 and feeds a signal current back to thebattery undergoing test 24. Summation circuitry 26 combines theresulting signal voltage 28 developed thereby across battery 24 with aperiodic square-wave signal voltage 30.

In the embodiment disclosed in FIG. 3, the periodic square-wave signalvoltage 30 is formed by the action of oscillator 32, chopper switch 34,and dc correction amplifier (Cor Amp) 36. The oscillation frequency ofoscillator 32 may, for example, be 100 Hz. The voltage applied to input38 of dc correction amplifier 36 is the dc terminal voltage of battery24. By virtue of the fact that the electronic apparatus disclosed inFIG. 3 draws very little load current from the battery, this terminalvoltage is essentially the battery's open-circuit (unloaded) terminalvoltage V_(o). Signal output 40 of dc correction amplifier 36 is a dcvoltage derived from V_(o) having a voltage level that is inverselyrelated to V_(o) --and hence inversely related to the state-of-charge ofbattery 24. This derived dc voltage 40 is repetitively interrupted bychopping switch 34 whose control input 42 is activated by the output ofoscillator 32. The chopped dc voltage thus comprises a periodicsquare-wave signal voltage 30 having a voltage amplitude that isinversely related to V_(o), and hence inversely related to thestate-of-charge of battery 24. This signal voltage 30 is presented tosummation circuitry 26 along with the signal voltage 28 developed acrossbattery 24. The resulting composite signal voltage 44 at the output ofsummation circuitry 26 is then capacitively coupled to input 20 ofhigh-gain amplifier cascade 12 by means of capacitive coupling network46.

As has been fully explained in U.S. Pat. No. 4,816,768, the voltage atoutput 10 of high-gain amplifier cascade 12 comprises a constant dc biascomponent along with an ac signal component that is proportional to thedynamic conductance G_(x) of the battery undergoing test 24 as well asto the level of the square-wave signal voltage 30. The constant dc biascomponent is ignored while the variable ac signal component is detectedand accurately converted to a dc signal voltage by synchronous detector48, synchronized to oscillator 32 by means of synchronizing path 50.

The dc signal voltage at output 52 of synchronous detector 48 passesthrough adjustable resistive network 54 to the input of dc-coupledoperational amplifier 56. Feedback path 58 of operational amplifier 56contains dc milliammeter 60. Accordingly, the reading of dc milliammeter60 is proportional to the dc signal voltage level at the output 52 ofsynchronous detector 48, and hence to the dynamic conductance G_(x) ofbattery 24. In addition, the constant of proportionality relating themilliammeter reading to G_(x) is determined by the value assumed byadjustable resistive network 54 as well as by the level of the signalvoltage at 30--and hence by the battery's state-of-charge as exemplifiedby its unloaded dc terminal voltage V_(o).

By utilizing an appropriate fixed resistance value in resistive network54 and then calibrating milliammeter 60 in battery measuring unitnumbers that are proportional to the battery's dynamic conductance, theembodiment disclosed in FIG. 3 will emulate the direct reading batterytester disclosed in U.S. Pat. No. 3,873,911. In addition, as is fullytaught in U.S. Pat. No. 4,816,768, the resistance value of resistivenetwork 54 which brings the reading of dc milliammeter 60 to aparticular fixed value is directly proportional to the dynamicconductance of battery 24. Hence, by calibrating resistive network 54 intraditional battery rating units, and then designating "pass" and "fail"regions on the face of milliammeter 60, the embodiment disclosed in FIG.3 will also emulate the "pass-fail" battery testing device disclosed inU.S. Pat. No. 3,909,708. Furthermore, one can employ a switch to selecteither a fixed-valued resistive network 54 or an adjustable-valuednetwork 54 and can arrange both a number scale and "pass-fail" regionson the face of milliammeter 60. One can therefore realize both adirect-reading battery tester and a "pass-fail" battery tester with asingle device.

For either emulation, the amplitude of the detected signal at the output52 of synchronous detector 48 is directly proportional to the amplitudeof the square-wave signal 30 at the output of chopper switch 34. Hence,both the level of the numerical quantity displayed during direct-readingoperation as well as the relative qualitative assessment provided in"pass-fail" operation are influenced by the battery's "state-of-charge",as exemplified by its unloaded terminal voltage V_(o). In order for thisdisplayed information to be independent of the battery'sstate-of-charge, one must require V_(out), the dc output voltage at 40of dc correction amplifier 36, to be proportional to the reciprocal ofG_(x) (V_(o)). Under these conditions, V_(out) can be written as:##EQU2## is an appropriate state-of-charge "correction factor" imposedby correction amplifier 36. Rearranging Equation 2 leads to: ##EQU3##which shows that F(V_(o)) may be simply regarded as the dc outputvoltage of amplifier 36 normalized with respect to the corresponding dcoutput voltage obtained with a fully-charged battery; i.e., a batteryfor which V_(o) =12.6 volts.

In addition to providing a dc signal output 40, the dc correctionamplifier 36 also provides a "Chopper Disable" output 62 and an LEDoutput 64. These two additional outputs become activated whenever thebattery's terminal voltage V_(o), and hence its state-of-charge, is toosmall for an accurate dynamic conductance test to be made. Under thesespecial conditions, chopper switch 34 becomes disabled so that noqualitative or quantitative information is displayed to the user.Instead, LED 66 lights to indicate to the user that the battery must berecharged before it can be tested.

FIG. 4 displays a graphical plot of the state-of-charge correctionfactor F(V_(o)) obtained by taking the reciprocal of the empirical[G_(x) (V_(o))/G_(x) (12.6)] curve disclosed in FIG. 2. A four-segmentpiecewise-linear approximation to this empirical curve is disclosed inFIG. 5. The parameters which specify the four breakpoints of thispiecewise-linear approximation are listed in Table I.

                  TABLE I                                                         ______________________________________                                        PIECEWISE-LINEAR APPROXIMATION PARAMETERS                                     Breakpoint   V.sub.o (Volts)                                                                        Correction Factor-F                                     ______________________________________                                        A            12.60    1.00                                                    B            12.15    1.21                                                    C            11.80    1.78                                                    D            11.60    2.91                                                    ______________________________________                                    

The piecewise-linear input-output relationship of FIG. 5 is implementedby the transfer function of the dc correction amplifier circuitembodiment disclosed in FIG. 6. Referring now to FIG. 6, the dccorrection amplifier contained generally in block 36 comprises theinterconnection of four operational amplifiers, 70, 72, 74, and 76 alongwith comparator 78. Circuit input lead 38 connects to the positiveterminal of the battery 24 under test, while the negative batteryterminal is grounded. By virtue of the fact that very little current isdrawn from battery 24, the circuit's input voltage at 38, V_(in),measured with respect to ground, is essentially equal to the battery'sopen-circuit terminal voltage V_(o).

Within the dc correction amplifier circuit disclosed in FIG. 6, aconstant reference voltage V_(R) is established by means of voltagereference diode 80 receiving operating current through series resistor82. Reference voltage V_(R) may, for example, be 2.5 volts. V_(R) isfurther operated on by a voltage divider chain comprising resistors 84,86, 88, and 90. Accordingly, the voltage level applied to thenoninverting inputs of operational amplifiers 70 and 72 is V_(R), whileincreasingly smaller fractions of reference voltage V_(R) are applied tothe noninverting inputs of operational amplifiers 74 and 76 and to theinverting input of comparator 78, respectively. In addition to thesefixed voltage levels, a variable voltage V_(x), that is proportional tobattery voltage V_(o) is derived from V_(in) by means of voltage dividerresistors 92 and 94. This variable voltage is applied directly to thenon-inverting input of comparator 78 and to the inverting inputs ofoperational amplifiers 72, 74, and 76 through resistors 98, 102, and106, respectively.

The outputs of the four operational amplifiers, 70, 72, 74, and 76, areconnected to a common output bus, V_(out), through the four diodes, 108,110, 112, and 114, respectively. Because of the operation of these fourdiodes, only one of the operational amplifiers will be active at any onegiven time--the amplifier having the largest (most positive) outputvoltage. That operational amplifier alone will be connected to theoutput bus and will thus be controlling the output voltage V_(out). Theother three operational amplifiers, those having smaller outputvoltages, will be disconnected from the output bus by virtue of theirhaving reverse-biased diodes in their output circuits.

Operational amplifier 70 has its inverting input connected directly tothe output bus and is therefore configured as a unity-gainvoltage-follower amplifying the reference voltage V_(R). Operationalamplifiers 72, 74, and 76 utilize feedback resistors and are configuredas inverting amplifiers; each amplifying the variable voltage V_(x) ;and each providing a negative incremental voltage gain given,respectively, by the appropriate resistance ratio {R(96)/R(98)},{R(100)/R(102)}, or {R(104)/R(106)}.

The circuit of FIG. 6 functions as follows: For V_(in) >V_(A) =12.6volts, the output voltage of operational amplifier 70 will be largerthan the output voltages of the other three operational amplifiers.Accordingly, the output bus will be controlled by the unity-gainvoltage-follower amplifier 70 so that V_(out) =V_(R). This region ofconstant output-voltage is represented by segment 1 in thepiecewise-linear transfer function displayed in FIG. 5.

When V_(in) has decreased to V_(A) =12.6 volts, V_(x) will have becomesufficiently less than V_(R) that the output of inverting amplifier 72will equal that of amplifier 70. Thus, for V_(in) <V_(A), diode 108 willbe reverse biased while diode 110 will be forward biased, and amplifier72 will control the output bus. Due to the amplification of invertingamplifier 72, further decreases in V_(in) will cause V_(out) to increasewith incremental gain or "slope" of -{(R96)/R(98)}. This region ofamplification, which continues until V_(in) =V_(B), is represented bysegment 2 in FIG. 5.

When V_(in) has decreased to V_(B), V_(x) will have decreasedsufficiently that the output of inverting amplifier 74 will exceed thatof amplifier 72. Diode 110 will therefore be reverse biased while diode112 will be forward biased, and amplifier 74 will now control the outputbus. Due to the amplification of inverting amplifier 74, furtherdecreases in V_(in) will cause V_(out) to increase with the largerincremental gain or "slope" of -{R(100)/R(102)}. This region ofamplification continues until V_(in) =V_(c) and is represented bysegment 3 in FIG. 5.

When V_(in) has decreased to V_(c), V_(x) will have decreasedsufficiently that the output of inverting amplifier 76 will exceed thatof amplifier 74. Diode 112 will therefore be reverse biased while diode114 will be forward biased. Thus, amplifier 76 will now control theoutput bus. Due to the amplifying action of inverting amplifier 76, anyfurther decreases in V_(in) will cause V_(out) to increase with thestill larger incremental gain or "slope" -{R(104)/R(106)}. This regionof largest amplification is represented by segment 4 in FIG. 5.

Finally, for V_(in) <V_(D), the derived voltage V_(x) will be less thanthe tapped-down reference voltage existing at the point ofinterconnection of resistors 88 and 90. Under these special conditions,the noninverting input of comparator 78 will be at a lower potentialthan the inverting input thus causing comparator 78's output to be in a"low" state. As a consequence, LED 66 will be lit to provide anindication to the user that the battery must be recharged before it canbe tested. In addition, output line 62 will be in a "low" state, thusdisabling chopper switch 34 and preventing any qualitative orquantitative dynamic conductance information from being conveyed to theuser.

FIG. 7 discloses a complete schematic diagram of a first embodiment ofan improved electronic battery testing/monitoring device with automaticstate-of-charge compensation configured for testing/monitoring 12-voltbatteries in accordance with the present invention. Operationalamplifiers 120, 122, 124, and 126 comprise four elements of a quadoperational amplifier integrated circuit, IC1. Bilateral analog switches34 and 128 comprise two elements of a quad CMOS bilateral switchintegrated circuit, IC2. Operational amplifiers 70, 72, 74, and 76comprise four elements of a quad operational amplifier integratedcircuit, IC3. Comparator 78 comprises one element of a quad comparatorintegrated circuit IC4. All four integrated circuits, IC1, IC2, IC3, andIC4 are powered by means of common power connections, V⁺ 130 and V⁻ 132,connected to the battery undergoing test 24 through battery contacts 134and 136, respectively.

High-gain amplifier cascade 12 of FIG. 3 comprises operational amplifier120 and npn transistor 138 connected as an emitter follower. Resistor140 conducts a dc bias voltage to the noninverting (+) input ofoperational amplifier 120 from voltage divider resistors 142 and 144which are connected to battery 24 through battery contacts 146 and 148.The output voltage of high-gain amplifier cascade 12 is establishedacross external-path feedback resistor 22. An internal feedback pathcomprising resistors 150 and 152 conducts the dc voltage at the commonconnection between the emitter of npn transistor 138 and resistor 22 tothe inverting (-) input of operational amplifier 120. Resistors 150 and152 along with capacitor 154 comprise low-pass filter 18 of FIG. 3.

The ac signal voltage developed across battery 24 is sensed at batterycontacts 146 and 148 and added in series to an input signal voltagecomponent established across viewing resistor 156. The resultantcomposite ac signal voltage is coupled to the differential input ofoperational amplifier 120 by means of a capacitive coupling networkcomprising capacitors 158 and 160. A feedback current that isproportional to the voltage established across resistor 22 passesthrough battery 24 by means of external feedback path conductors 162 and164 along with battery contacts 134 and 136.

An ac square-wave input signal voltage is established across viewingresistor 156 and is formed by the action of oscillator 32, chopperswitch 34, and correction amplifier 36. Oscillator 32, which generates a100 Hz square-wave synchronizing signal, is a conventional astablemultivibrator comprising operational amplifier 122 along with resistors168, 170, 172, 174, and capacitor 176. The synchronizing output signalof oscillator 32 is conducted to the control input of chopper switch 34through resistor 178. Accordingly, chopper switch 34 turns on and offperiodically at a 100 Hz rate. The signal terminals of chopper switch118 interconnect the dc signal output 40 of correction amplifier 36 withthe input lead of trimmer potentiometer 180 used for initial calibrationadjustment. The signal voltage across trimmer potentiometer 180therefore comprises a 100 Hz square wave having amplitude proportionalto the dc output voltage of correction amplifier 36. A signal currentproportional to the signal output voltage of trimmer potentiometer 180passes through injection resistor 184 and is injected into viewingresistor 156 thereby developing a 100 Hz signal voltage across viewingresistor 156. By virtue of the action of correction amplifier 36described with reference to FIG. 6, the signal voltage across viewingresistor 156 will contain an automatic correction for thestate-of-charge of the battery undergoing test. If, however, thebattery's state-of-charge is too low for an accurate battery assessmentto be made, the correction amplifier's output lines 62 and 64 will be inlogic low states. These output lines will, in turn, pull the controlinput of chopper switch 34 low and pull the cathode of LED 66 low. As aresult, chopper switch 34 will be disabled so that no ac signal will beinjected into viewing resistor 156, and LED 66 will light to indicate tothe user that the battery must be recharged before a dynamic conductancetest can be performed.

Analog switch 128 along with operational amplifier 124, which isconnected as an integrator, comprise synchronous detector 48 of FIG. 3.Resistor 194 and bypass capacitor 196 comprise a low-pass filter whichbiases the noninverting input of operational amplifier 124 to thevoltage level of the dc bias component developed across feedbackresistor 22. A signal current derived from the total voltage at thecommon connection between resistor 22 and transistor 138 passes throughresistor 198 and analog switch 128 to the inverting input of operationalamplifier 124. This signal current is periodically interrupted at theoscillator frequency by virtue of the control input of analog switch 128being connected to the synchronizing output of oscillator 32. Resistor200 provides negative dc feedback to operational amplifier 124.Integration capacitor 202 serves to smooth the detected voltage signaloutputted by operational amplifier 124.

The noninverting input of operational amplifier 126 is biased to the dclevel of the noninverting input of operational amplifier 124 while theinverting input of operational amplifier 126 is connected to SPDTselector switch 206. Accordingly, a dc current proportional to thedetected signal voltage at the output of operational amplifier 124passes through milliammeter 60 to the output of operational amplifier116 by way of one of the two paths selected by selector switch 206. Withswitch 206 in position 1, the meter current passes through fixedresistor 208. Under these conditions, the disclosed invention emulates adirect reading battery testing device providing a quantitative outputdisplayed in battery measuring units that are proportional to thedynamic conductance of battery 24. With switch 206 in position 2, themeter current passes through fixed resistor 210 and variable resistor212. Under these conditions the disclosed invention emulates aqualitative, "pass-fail", battery testing device having a manuallyadjusted battery rating scale that is linearly related to the setting ofvariable resistance 212, and a rating offset that is determined by thevalue of fixed resistor 210.

The improved battery testing/monitoring device embodiment havingautomatic compensation for low state-of-charge disclosed in FIG. 7 isoperated as follows: The operator simply connects the device to thebattery undergoing test and selects one of the two positions of selectorswitch 206. If position 1 is selected, meter 60 will display thebattery's quantitative condition in appropriate battery measuringunits--with the displayed quantitative results having been automaticallyadjusted to conform with those of a fully-charged battery. If switch 206is in position 2, and variable resistance 212 has been set in accordancewith the battery's rating, meter 60 will display the battery'squalitative ("pass/fail") condition. Again, the displayed results willhave been automatically adjusted to conform with those of afully-charged battery. With either selection, if the battery'sstate-of-charge is too low for an accurate assessment to be made, noinformation will be displayed to the user. Instead, an LED will light toindicate to the user that the battery must be recharged before testing.

Table II contains a listing of component types and values for the firstembodiment of an improved electronic battery testing/monitoring devicewith automatic compensation for low state-of-charge disclosed in FIG. 7.

                  TABLE II                                                        ______________________________________                                        COMPONENT TYPES AND VALUES                                                    FOR CIRCUIT OF FIG. 7                                                         REFERENCE NUMBER     COMPONENT                                                ______________________________________                                        Semiconductor Devices                                                         120, 122, 124, 126   IC1 - LM324N                                             34, 128              IC2 - CD4066B                                            70, 72, 74, 76       IC3 - LM324N                                             78                   IC4 - LM339                                              80                   IC5 - LM336-.25                                          138                  TIP31C Power                                                                  Transistor                                               108, 110, 112, 114   1N4148 Diodes                                            66                   T-13/4 LED                                               Resistors - Ohms (1/4-W unless specified)                                     5 Watts              22Ω                                                82                   4.7K                                                     84                   5.36K                                                    86                   6.19K                                                    88                   6.04K                                                    90                   200K                                                     92                   2.25K                                                    94                   576                                                      96, 100, 104         1.00M                                                    98                   174K                                                     102                  49.9K                                                    106                  13.7K                                                    116, 142, 144        1.0K                                                     156, 210             100                                                      208                  470                                                      212                  500 Variable                                             180                  10K Trimpot                                              184                  470K                                                     140, 200             47K                                                      178, 194, 198        100K                                                     172                  150K                                                     174                  270K                                                     150, 152, 168, 170   1 Meg                                                    Capacitors - Mfd                                                              176                  0.022                                                    154, 158, 160, 196   0.47                                                     202                  1.0                                                      Meter                                                                         204                  1 mA dc                                                                       milliammeter                                             Switch                                                                        206                  SPDT                                                     ______________________________________                                    

FIG. 8 discloses a simplified block diagram of a second embodiment of animproved electronic battery testing/monitoring device with automaticcompensation for low state-of-charge. This embodiment eliminates thecorrection amplifier 36 and chopper switch 34 of the first embodimentdisclosed in block diagram form in FIG. 3. Instead, it contains amicroprocessor represented generally by block 220 of FIG. 8.Microprocessor block 220 includes all of the usual elements whichcomprise a microprocessor system such as the requisite logic elements, aclock oscillator, a random access memory, a firmware program containedin read-only memory, and, of course, the processor itself. With theembodiment of FIG. 8, the appropriate correction for low state-of-chargeis performed by microprocessor block 220 under the control of thefirmware program contained therein.

A description of operation of most of the elements of FIG. 8 parallelsthe description of operation of the embodiment disclosed in FIG. 3.Signals representative of the signal at output 10 of high-gain amplifiercascade 12 are fed back to input 20 of high-gain amplifier cascade 12 bymeans of two feedback paths; internal feedback path 14 and externalfeedback path 16. Internal feedback path 14 includes low pass filter(LPF) 18 and feeds a signal voltage directly back to input 20 ofhigh-gain amplifier cascade 12. External feedback path 16 containsresistive network 22 and feeds a signal current back to the batteryundergoing test 24. Summation circuitry 26 combines the resulting signalvoltage 28 developed thereby across battery 24 with a periodicsquare-wave signal voltage 30.

In the embodiment of FIG. 8, signal voltage 30 simply comprises theconstant output signal of oscillator 32. The oscillation frequency ofoscillator 32 may, for example, be 100 Hz. This periodic signal voltageis presented to summation circuitry 26 along with the signal voltage 28developed across battery 24. The resulting composite signal voltage 44at the output of summation circuitry 26 is then capacitively coupled toinput 20 of high-gain amplifier cascade 12 by means of capacitivecoupling network 46. Accordingly, the voltage at output 10 of high-gainamplifier cascade 12 comprises a constant dc bias component along withan ac signal component that is proportional to the dynamic conductanceG_(x) of the battery undergoing test 24. The constant dc bias componentis ignored while the variable ac signal component is detected andaccurately converted to a dc signal voltage by synchronous detector 48,synchronized to the oscillator by means of synchronizing path 50.

The dc signal level at output 52 of synchronous detector 50 isproportional to the battery's dynamic conductance G_(x). This analogvoltage is converted to a corresponding digital representation of G_(x)by analog to digital (A/D) converter 222 and then inputted tomicroprocessor block 220 through input port 224. In addition, thebattery's unloaded voltage V_(o) is connected via dc path 38 to theinput of analog to digital converter 226. A corresponding digitalrepresentation of V_(o) at the output of A/D converter 226 is therebyinputted to microprocessor block 220 through input port 228.

By programmed algorithmic techniques that are well-known to thoseskilled in the art, the microprocessor's firmware program utilizes thedigital representation of V_(o) to correct the digital representation ofG_(x) for the battery's state-of-charge. This can be done, for example,by inputting V_(o) to a "look-up table" whose output is thecorresponding correction factor F, and then multiplying G_(x) by theresulting factor F to obtain the corrected conductance value, G_(x)(12.6). Alternatively, the appropriate value of G_(x) (12.6) could becalculated directly by numerically evaluating the reciprocal of theempirical relationship disclosed in Equation 1.

In order to emulate of a quantitative-type electronic battery tester, anumerical value proportional to G_(x) (12.6) is outputted and displayedon a digital display such as 236 interfaced through output port 234, orprinted by a printer such as 240 interfaced to microprocessor 220through output port 238. In addition, whenever V_(o) is less than apredetermined minimum value, the firmware program suppresses thenumerical display and instead provides an indication to the user thatthe battery must be recharged before testing. This special informationcan, for example, be displayed by digital display 236, printed byprinter 240, or conveyed to the user by an LED 66 interfaced tomicroprocessor 220 through output port 242.

For emulation of a qualitative ("pass/fail") electronic battery tester,the battery's rating is first inputted to microprocessor 220 through aninput device such as a shaft encoder 230 interfaced to microprocessor220 through input port 232. A dial associated with shaft encoder 230 iscalibrated in battery rating units such as cold cranking amperes orampere-hours. By programmed algorithmic techniques that are well-knownto those skilled in the art, the microprocessor's firmware program thendirects microprocessor block 220 to compare the dynamic conductancecorrected for state-of-charge, G_(x) (12.6), with a reference valueappropriate to the inputted battery rating and to output the resultingpass/fail information to the user. This qualitative output informationcan, for example, be displayed by digital display 236, printed byprinter 240, or conveyed to the user by an LED 246 interfaced tomicroprocessor 220 through output port 244. Again, if V_(o) is less thana predetermined minimum value, the displayed information is suppressedand the user is informed that the battery must be recharged beforetesting. This special information can, for example, be displayed bydigital display 236, printed by printer 240, or conveyed to the user byLED 66.

FIG. 9 discloses a simplified block diagram of a third embodiment of animproved electronic battery testing/monitoring device with automaticcompensation for low state-of-charge. Like the embodiment disclosed inFIG. 8, this third embodiment employs a microprocessor block 220 toimplement the appropriate correction for low state-of-charge. It differsfrom the embodiment of FIG. 8, however, in that the hardware inputs adigital representation of the battery's dynamic resistance R_(x) tomicroprocessor 220 which then utilizes its firmware program to calculatethe reciprocal quantity, the battery's dynamic conductance G_(x)=1/R_(x), as well as to correct for the battery's state-of-charge.

The hardware disclosed in FIG. 9 functions as follows: Oscillator 32generates a periodic square-wave signal 42 which is inputted to directlyto current amplifier 244. The oscillation frequency of oscillator 32may, for example, be 100 Hz. The output of current amplifier 244, aperiodic signal current 246, then passes through battery 24. By virtueof the fact that the output resistance of current amplifier 244 is muchlarger than the battery's dynamic resistance R_(x), the amplitude ofsignal current 246 will be virtually independent of R_(x). Accordingly,the resultant ac signal voltage 248 appearing across the battery'sterminals will be directly proportional to the battery's dynamicresistance R_(x). Capacitive coupling network 250 couples the ac signalvoltage 248 to input 252 of voltage amplifier 254. This coupling networksuppresses the battery's dc terminal voltage but permits amplificationof the ac signal voltage by voltage amplifier 254. The output voltage256 of voltage amplifier 254 provides the input to synchronous detector48 which is synchronized to oscillator 32 by means of synchronizing path50. Accordingly, a dc signal voltage 52 appears at the output ofsynchronous detector 48 that is directly proportional to the battery'sdynamic resistance R_(x).

The analog voltage 52 is converted to a corresponding digitalrepresentation of R_(x) by analog to digital (A/D) converter 222 andthen inputted to microprocessor block 220 through input port 224. Inaddition, the battery's unloaded voltage V_(o) is connected via dc path38 to the input of analog to digital converter 226. A correspondingdigital representation of V_(o) at the output of A/D converter 226 isthereupon inputted to microprocessor block 220 through input port 228.

By programmed algorithmic techniques that are well-known to thoseskilled in the art, the microprocessor's firmware program directsmicroprocessor block 220 to invert the digital representation of R_(x)to obtain a digital representation of the battery's dynamic conductanceG_(x). It then utilizes the digital representation of V_(o) to correctthe digital representation of G_(x) for the battery's state-of-charge.This can be done, for example, by inputting V_(o) to a "look-up table"whose output is the corresponding correction factor F, and thenmultiplying G_(x) by the resulting factor F to obtain the correctedconductance value, G_(x) (12.6); or by computing G_(x) (12.6) directlyfrom the reciprocal of the empirical relationship disclosed inEquation 1. Alternatively, a temperature-corrected value of R_(x), R_(x)(12.6), can be computed first and then algorithmically inverted toobtain G_(x) (12.6).

In order to emulate a quantitative-type electronic battery tester, anumerical result proportional to G_(x) (12.6) is outputted and displayedon a digital display such as 236 interfaced through output port 234, orprinted by a printer such as 240 interfaced to microprocessor 220through output port 238. In addition, whenever V_(o) is less than apredetermined minimum value, the firmware program suppresses thenumerical display and instead provides an indication to the user thatthe battery must be recharged before testing. This information can, forexample, be displayed by digital display 236, printed by printer 240, orconveyed to the user by an LED 66 interfaced to microprocessor 220through output port 242.

For emulation of a qualitative ("pass/fail") type of electronic batterytester, the battery's rating is inputted to microprocessor 220 throughan input device such as a shaft encoder 230 interfaced to microprocessor220 through input port 232. A dial associated with shaft encoder 230 iscalibrated in battery rating units such as cold cranking amperes orampere-hours. By programmed algorithmic techniques that are well-knownto those skilled in the art, the microprocessor's firmware programdirects microprocessor block 220 to compare the computed quantity, G_(x)(12.6), with a reference quantity appropriate to the inputted batteryrating to determine whether the battery passes or fails. For a computedquantity larger than the reference quantity, the battery passes.Otherwise it fails. Alternatively, a comparison can be made between thecomputed quantity R_(x) (12.6) and a corresponding reference quantityappropriate to the inputted battery rating to determine whether thebattery passes or fails. For a computed quantity less than the referencequantity, the battery passes. Otherwise it fails. In either case, thisqualitative information is outputted and displayed by digital display236, printed by printer 240, or conveyed to the user by an LED 246interfaced to microprocessor 220 through output Port 244. Again, ifV_(o) is less than a predetermined minimum value, the display ofqualitative information is suppressed and the user is informed that thebattery must be recharged before testing. This special information can,for example, be displayed by digital display 236, printed by printer240, or conveyed to the user by LED 66.

Although three specific modes for carrying out the invention hereof havebeen described, it should be understood that many modifications andvariations can be made without departing from what is regarded to be thescope and subject matter of the invention. For example, the inventionmay comprise a single, self-contained, instrument that is temporarilyconnected to the battery to test the battery on-site. Alternatively, thedevice may comprise a monitoring device that is semi-permanentlyconnected to the battery to provide continuous monitoring of thebattery's condition at a remote location. In this latter case, thedevice will probably be separated into two parts--one part connected tothe battery and located at the battery's site; the other part containingthe remote display and located at the remote location. The divisionbetween the two parts can be made somewhat arbitrarily. However, Icontend that all such divisions, modifications, and variations fallwithin the scope of the invention disclosed herein and are thereforeintended to be covered by the appended claims.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An electronic device for assessing the conditionof an electrochemical cell or battery having a dynamic conductance andan open-circuit voltage comprising:means operably connected to said cellor battery for detecting said dynamic conductance and for generating asignal proportional thereto; means operably connected to said cell orbattery for sensing said open-circuit voltage; correction means coupledto said means for detecting said dynamic conductance and directlyelectrically coupled to said means for sensing said open-circuitvoltage, said correction means for responding to said open-circuitvoltage by adjusting the level of said signal in accordance with saidopen-circuit voltage; and, means for displaying an assessment of saidcell or battery in accordance with the adjusted level of said signal. 2.An electronic device as in claim 1 wherein said correction means adjustssaid level of said signal in inverse correspondence with the value ofsaid open-circuit voltage relative to a fully-charged value.
 3. Anelectronic device as in claim 2 wherein said correction means comprisesa correction amplifier having an input voltage and an output voltage,said input voltage being derived from said open-circuit voltage and saidoutput voltage being proportional to said adjusted level of said signal.4. An electronic device as in claim 3 wherein said correction amplifiercomprises a reference voltage, a plurality of operational amplifier, aplurality of diodes, and a plurality of resistors interconnected toprovide a piece-wise linear transfer function relating said outputvoltage to said input voltage.
 5. An electronic device for assessing thecondition of an electrochemical cell or battery having an internalresistance and a dc terminal voltage comprising:means directlyelectrically coupled to said electrochemical cell or battery forgenerating a time-varying first signal inversely related to said dcterminal voltage; current generating means coupled to saidelectrochemical cell or battery and to said means for generating atime-varying first signal, said current generating means for producing asecond signal directly proportional to said first signal and inverselyproportional to said internal resistance; and means coupled to saidcurrent generating means for sensing said second signal and for relatingsaid second signal to said condition of said electrochemical cell orbattery.
 6. An electronic device as in claim 5 wherein said means forgenerating a time-varying first signal includes a nonlinear dc amplifiermeans for amplifying said dc terminal voltage and further includes achopper means for chopping a dc output of said nonlinear dc amplifiermeans to produce said time-varying first signal.
 7. An electronic deviceas in claim 6 wherein said nonlinear dc amplifier means has apiecewise-linear transfer function.
 8. An electronic device forassessing the condition of an electrochemical cell or battery having adc terminal voltage comprising:means directly electrically coupled tosaid electrochemical cell or battery for generating a time-varying inputsignal inversely related to said dc terminal voltage; high-gainamplifier means for providing an output signal; internal feedback meansincluding low-pass filter means for coupling said output signal to theinput of said high-gain amplifier means; external feedback meansincluding feedback resistor means for coupling said output signal tosaid electrochemical cell or battery; capacitive coupling means forcoupling said input signal and a time-varying voltage across saidelectrochemical cell or battery to said input of said high-gainamplifier means; and, means coupled to said high-gain amplifier meansfor sensing said output signal and for relating said output signal tosaid condition of said electrochemical cell or battery.
 9. An electronicdevice as in claim 8 wherein said means for generating a time-varyinginput signal includes a nonlinear dc amplifier means for amplifying saiddc terminal voltage and further includes a chopper means for chopping adc output of said nonlinear dc amplifier means to produce saidtime-varying input signal.
 10. An electronic device as in claim 9wherein said nonlinear dc amplifier means has a piecewise-lineartransfer function.
 11. An electronic device for assessing the conditionof an electrochemical cell or battery having a dynamic parameter and anopen-circuit voltage comprising:means operably connected to said cell orbattery for measuring said dynamic parameter; means operably connectedto said cell or battery for sensing said open-circuit voltage;correction means coupled to said means for measuring said dynamicparameter and directly electrically coupled to said means for sensingsaid open-circuit voltage, said correction means for responding to saidopen-circuit voltage by adjusting a measured dynamic parameter value inaccordance with said open-circuit voltage to obtain a corrected dynamicparameter value; and means for displaying an assessment of saidcondition of said electrochemical cell or battery in conformance withsaid corrected dynamic parameter value.
 12. An electronic device inaccordance with claim 11 including means for providing a specialindication when said open-circuit voltage is less than a predeterminedvalue and further including means for suppressing said assessment whensaid open-circuit voltage is less than a predetermined value.
 13. Anelectronic device in accordance with claim 11 wherein said dynamicparameter is dynamic conductance and said correction means includescorrection amplifier means having an input voltage and an outputvoltage, said input voltage being proportional to said open-circuitvoltage and said output voltage being proportional to the ratio of saidcorrected dynamic conductance value to said measured dynamic conductancevalue.
 14. An electronic device in accordance with claim 11 wherein saiddynamic parameter is dynamic conductance and said correction meanscomprises a firmware correction program implemented by microprocessormeans and wherein digital representations of said open-circuit voltageand said dynamic conductance are both inputted to said microprocessorand combined algorithmically to obtain said corrected dynamicconductance value based upon said firmware correction program.
 15. Anelectronic device in accordance with claim 11 wherein said dynamicparameter is dynamic resistance and said correction means comprises afirmware correction program implemented by a microprocessor, and whereindigital representations of said open-circuit voltage and said dynamicresistance are both inputted to said microprocessor and combinedalgorithmically to obtain said corrected dynamic resistance value basedupon said firmware correction program.
 16. An electronic device inaccordance with claim 11 wherein said assessment comprises numbersproportional to said corrected dynamic parameter value.
 17. Anelectronic device in accordance with claim 11 wherein said assessmentcomprises a qualitative assessment in conformance with said correcteddynamic parameter value relative to a reference dynamic parameter value.18. An electronic device in accordance with claim 17 wherein saidelectrochemical cell or battery has an electrical rating, saidelectronic device includes means for inputting the value of said rating,and said reference dynamic parameter value is determined by theparticular value of said electrical rating thus inputted.
 19. Anelectronic device for assessing the condition of an electrochemical cellor battery having a dynamic conductance, an open-circuit voltage, and astate-of-charge comprising:means operably connected to said cell orbattery for determining a digital representation of said dynamicconductance; means directly electrically connected to said cell orbattery for determining a digital representation of said open-circuitvoltage; microprocessor means for implementing a firmware correctionprogram, said microprocessor means directly electrically coupled to saidmeans for determining a digital representation of said dynamicconductance and to said means for determining a digital representationof said open-circuit voltage and algorithmically combining said digitalrepresentation of said dynamic conductance with said digitalrepresentation of said open-circuit voltage to obtain an assessmentresult representative of said dynamic conductance corrected to representits presumed value at 100% state-of-charge based upon said firmwarecorrection program; and means for displaying said assessment result. 20.An electronic device as in claim 19 wherein said assessment resultcomprises numbers proportional to said dynamic conductance corrected torepresent its presumed value at 100% state-of-charge.
 21. An electronicdevice as in claim 19 wherein said assessment result comprises aqualitative result determined in accordance with the value of saiddynamic conductance corrected to represent its presumed value at 100%state-of-charge relative to a reference value.
 22. An electronic deviceas in claim 21 wherein said electrochemical cell or battery has anelectrical rating and said electronic device includes means forinputting said electrical rating to said microprocessor means, saidreference value being determined by the particular value of saidelectrical rating thus inputted.
 23. An electronic device for assessingthe condition of an electrochemical cell or battery having a dynamicresistance, an open-circuit voltage, a state-of-charge, and anelectrical rating, comprising:means operably connected to said cell orbattery for determining a digital representation of said dynamicresistance; means directly electrically connected to said cell orbattery for determining a digital representation of said open-circuitvoltage; microprocessor means for implementing a firmware correctionprogram, said microprocessor means directly electrically coupled to saidmeans for determining a digital representation of said dynamicresistance and to said means for determining a digital representation ofsaid open-circuit voltage and algorithmically combining said digitalrepresentation of said dynamic resistance with said digitalrepresentation of said open-circuit voltage based upon said firmwarecorrection program thereby evaluating a reciprocal dynamic resistancecorrected to represent its presumed value at 100% state-of charge; meansfor inputting said electrical rating to said microprocessor means fordetermining a reference quantity therefrom; means for comparing saidreference quantity with said reciprocal dynamic resistance corrected torepresent its presumed value at 100% state-of-charge; and means fordisplaying a qualitative assessment of said condition of saidelectrochemical cell or battery in accordance with said comparison. 24.An electronic device as in claim 23 including means for suppressing saidqualitative assessment and for providing a special indication when saidopen-circuit voltage is less than a predetermined value.
 25. Anelectronic device for assessing the condition of an electrochemical cellor battery having a dynamic resistance, an open-circuit voltage, astate-of-charge, and an electrical rating comprising:means operablyconnected to said cell or battery for determining a digitalrepresentation of said dynamic resistance; means directly electricallyconnected to said cell or battery for determining a digitalrepresentation of said open-circuit voltage; microprocessor means forimplementing a firmware correction program, said microprocessor meansdirectly electrically coupled to said means for determining a digitalrepresentation of said dynamic resistance and to said means fordetermining a digital representation of said open-circuit voltage andalgorithmically combining said digital representation of said dynamicresistance with said digital representation of said open-circuit voltagebased upon said firmware correction program thereby evaluating a dynamicresistance corrected to represent its presumed value at 100%state-of-charge; means for inputting said electrical rating to saidmicroprocessor means for determining a reference quantity therefrom;means for comparing said reference quantity with said dynamic resistancecorrected to represent its presumed value at 100% state-of-charge; and,means for displaying a qualitative assessment of said condition of saidelectrochemical cell or battery in accordance with said comparison. 26.An electronic device as in claim 25 including means for suppressing saidqualitative assessment and for providing a special indication when saidopen-circuit voltage is less than a predetermined value.